The string are expensive, yes, but they last me so long it's worth it.
I once had a set of these strings on my 12 string guitar for over a decade, and only changed them after a guitar set up (I hate changing strings, especially on a 12 string!).
They stay in tune, and the sound doesn't dull to my ears. Coating the strings in 24 k gold does definitely give them a "played in" more mellow tone, but I like that as I don't like the "zingy" overtones of new strings.
To me the only con is the price, but they are cost effective because they sound good, and stay in tune for so long!!